A need to continuously measure the level of a fluid exists in many commercial and military applications. For example, fluid-level sensors are commonly used in the fuel tanks of aircraft, automobiles, and trucks. Fluid-level sensors are also used to monitor fluid levels within tanks utilized for fuel dispensing, wastewater treatment, chemical storage, food processing, etc.
Electrical fluid-level sensors present safety-related issues in many applications. For example, electrical fluid-level sensors have the potential to generate sparks, and thus present an explosion hazard when used in the presence of flammable fluids. In particular, the electrical current associated with an electrical fluid-level sensor has the potential to introduce a spark due to, for example, chaffed insulation on the wiring that carries electrical current to or from the sensor. A spark can ignite explosive vapors that may be present in the tank in which the sensor is located.
Moreover, electrical sensors are susceptible to signal degradation in the presence of electromagnetic interference.
Electrical fluid-level sensors can include a float mechanically or magnetically coupled to an external gauge. Alternatively, electrical fluid-level sensors can operate on the principle that the dielectric constant between electrical conductors immersed or partially immersed in a fluid changes with the fluid level. This type of sensor, however, when used to detect fuel levels, can lose accuracy as the amount of water and other contaminates in the fuel increases.
The presence of contaminates in the fluid can result in additional problems. For example, water is often present in aircraft fuel tanks due to factors such as the introduction of contaminated fuel into the tank, condensation within the tank, and infiltration during fueling in adverse weather conditions. Water-contaminated fuel can result in degraded engine performance, and in extreme cases, can cause a complete engine stoppage.
An ongoing need therefore exists for a system that can determine the level and/or type of a fluid in a tank or other container without introducing electrical current into the tank or container, and that can function in a satisfactory manner in the presence of contaminates and/or electromagnetic interference.